Variable stroke motor



D. M. BERGES 2,298,457

VARIABLE STROKE MOTOR Filed April 18, 1941 W/NDSH IELD WIPE R ARM INVENTOR onald MBrg'qs Patented Oct. 13,1942

UNITED STAT-ES PATENT OFFICE s'rnonuMorort Donald M. Berges, Tenlafly, N. J., assignor. to

Bendix Aviation Corporation, South Bend, Ind.,

a corporation of Delaware Application April 18, 1941, Serial No. 389,253

3 Claims.

This invention relates to hydraulic motors, and more particularly to a reciprocating motor having a variable stroke. 1 It is an object of the present invention to provide a hydraulic motorwherein the direction of the working stroke may be automatically reversed upon the increase of pressure beyond a predetermined value.

Other objects of the invention include the provision of a hydraulic motor wherein the working stroke may be reversed at any time prior to its normal complete stroke upon the encountering of an obstruction, and the provisionof a hydraulic motor wherein the presence of an obstruction during the normal working stroke automatically limits and efiects the reversal of the working stroke. 1 Other objects will appear from a study of the following specification when made in conjunction with the attached drawing, wherein the single figure of the drawing is an elevational view, partly in section, of one embodiment of the present invention.

A motor housing III of cast steel, aluminum or other suitable material, contains a double ended cylinder II having a fluid port I2 at one end and a second fluid port I3 at the other end thereof. A working piston I4, of any suitable design, is mounted for reciprocal movement within cylinder II and has attached thereto a piston rod I5,

.valve members I8 and I9 by means of coiled springs 25 and '26, respectively.v Outward motion cylinder II through either of the ports ohmssageways 33 and 34. As shown in the drawing,

passageway 33 is open to cylinder I I, and oil will be admitted through this passageway into cylinder II. Relief outlets or exhaust ports 35 and 36 are afforded for the return of oil through conduits 3! and 38 to a sump 39.

The operation of the hydraulic motorshown will be readily understood; Oil under pressure flows from pump 3| through conduit 32 and into cylinder II through passageway 33, forcing piston I4 to the extreme right of cylinder I I. When piston I4 reaches the endof its right-hand travel, continued flow of oil from pump 3I results in a greatly increased pressure on the left side of cylinder I I, and this pressure is transmitted through fluid port E2 to the face of auxiliary piston 23,

, forcing this piston to compress spring 25. This spring (as well as spring 26) has a pre-selected resilient value so that upon compression by movement of piston 23, the restraining force of detent 29 is overcome, and valve 58 is released With a snap action to close off passageway 33 from oil inlet-.32. This movement of valve I8 carries indentation 28 of valve I9 into engagement'with detent and also carries the end face 22 of the of auxiliary pistons 23 and 24 along valve rod 20 is limited by the head members 2| and 22; The bottom portion of the periphery of valve member I8 contains a small indentation '21, and a corresponding indentation 28 is formed in valve member I9. Also, for cooperation with these indentations, detent members 29 and 30 are placed within recesses in motor housing III. These detents may be of any conventional type such as the springloaded balls ihdicated in the drawing.

Oil or other-fluid under pressure from a source such as pump 3| is carried through conduit 32 valve rod against the inside wall of housing I0. In this position, oil flows into cylinder II. through passageway 34, causing piston I4 tomove to the left until it abuts with the internal end wall of cylinder II. As pump 3| continues to function,

of auxiliary piston 24 increases, causing spring 26 to be compressed, and eventually,-upon sufficient may be provided. Asshown, valve 40 has a passageway 42 which, in the position illustrated, permits pressure from pump 3I to be imparted "to the motor through intake conduit 32.' If it is the bottom portion of conduit 32. With valve 40 in this position, pump 3| returns oil in its output into valve chamber I1 and'may be admitted to 6 to the sump 39, by way of exhaust conduit 31.

has general application, it is particularly useful in the actuation of an aircraft windshield wiper, principally since the accumulation of ice or any other obstruction encountered in flight which tends to limit the full stroke of piston [4 does not prevent the continued use of the motor to drive the windshield wiper through a path of shortened stroke. For example, if we assume that piston Id, at the position shown in the drawing, is prevented from moving further to the right by the formation of ice on the windshield of an airplane, the increase of hydraulic pressure against the face of piston 23 will cause a reversal of fluid flow in the manner above described so that the windshield wiper l6 may still be used to clean a' restricted portion of the windshield.

The use of the motor of the present invention to drive a windshield wiper is to be taken as only one example of the possible applications to which the invention may be put. The invention is to be limited, therefore, not by the particular embodiment shown and described, but by the scope of the appended claims.

I claim:

1. In a hydraulic motor including a piston having a working stroke in two directions of travel, 'valve means for permitting the travel of said piston in each direction and for reversing the direction of travel of said piston, said valve means including a valve rod, two spaced valve members flxed to said rod, two auxiliary piston members slidably carried by said valve rod and maintained resiliently spaced from said valve members, a valve and piston chamber enclosing said valve members and auxiliary pistons, detent means for selectively holding one of said valve members in a fixed position, and fluid ports opening on opposite sides of said pistons, whereby, upon the increase of fluid pressure beyond a predetermined value, said auxiliary pistons will be selectively urged toward its corresponding valve member with a force suflicient to free said valve member from said detent and move it to reverse the direction of fluid flow against said piston.

2. In a hydraulic motor including a piston having a working stroke in two directions of travel, valve means for permitting the travel of said piston ineach direction and for reversing the direction of travel of said piston, said valve means including a valve rod, a valve member fixed to said rod, an auxiliary piston member slidably carried by said valve rod and maintained resiliently spaced from said valve, member, a chamber enclosing said valve and auxiliary piston means, detent means for holding said valve member in a fixed position, and a fluid port open to said piston and to said auxiliary piston, whereby, upon the increase of fluid pressure beyond a predetermined value, said auxiliary piston will be urged toward said valve member with a force suflicient to free said valve member from said detent and moveit to change the direction of fluid flow with respect to said piston.

3. A hydraulic motor comprising a housing, a' double-ended cylinder within said housing, a

working piston, a piston rod connected thereto, a fluid port at each end of said cylinder, a valve 'c hamber in said housing, a valve member associated with each of said ports, a source of fluid pressure-connected to said housing, reilef 'ports in said chamber, a valve rod rigidly connected to said valve members, an auxiliary piston slid- DONALD M. BERGES. 

